Endosomal/lysosomal targeting of a single helper T-cell epitope of an intracellular bacterium by DNA immunisation induces a specific T-cell subset and partial protective immunity in vivo.

We evaluated here the effect of the intracellular targeting of a helper T-cell (Th) epitope, literiolysin O 215-226 derived from Listeria monocytogenes, on induction of a specific Th by gene gun immunisation. Immunisation of C3H/He mice with pE215LAMP plasmid encoding the Th epitope fused with the endosomal/lysosomal targeting signal of lysosome-associated membrane protein (LAMP)-1 gave the epitope-specific proliferative responses of CD4(+) T lymphocytes. In addition, specific interferon-gamma production from the splenocytes was observed. Concomitantly, pE215LAMP-immunised mice showed moderate, but significant protective immunity against listerial challenge. These results suggest that the intracellular targeting of a Th epitope to endosomal/lysosomal compartments by DNA immunisation is useful for eliciting a specific Th subset in vivo.